In recent years, in a wireless communication system (a cellular system) including a wireless base station such as a mobile telephone system, discussion on next generation wireless communication technologies has been performed to further enhance high speed and high capacity wireless communication. For example, communication standards called Long Term Evolution (LTE) and communication standards called LTE-Advanced (LTE-A) that is based on an LTE wireless communication technology have been proposed by the 3rd Generation Partnership Project (3GPP) that is a standard body. “LTE” is hereinafter defined as including other wireless communication systems that are enhancements of LTE and LTE-A, as well as LTE and LTE-A, unless otherwise specified.
LTE (LTE-A) includes various technologies, one of which is device-to-device (D2D) communication. The D2D communication is so-called inter-terminal communication in the 3GPP. For example, many wireless terminals, although positioned a short distance away from one another, normally perform communication through a wireless base station in LTE. In contrast, according to the D2D communication, wireless terminals can perform direct communication without the wireless base station being involved.
According to the D2D communication, the communication among the wireless terminals is possible even in a case where the communication in which the wireless base station is involved is not performed, for example, when a disaster occurs (this is defined as a public safety scenario in the 3GPP). Furthermore, it is thought that the D2D communication promisingly finds application in machine type communication (MTC) as well that is equivalent to so-called machine-to-machine (M2M) communication in the 3GPP. It is thought that in the MTC which has been discussed in the 3GPP, inter-terminal communication is performed through the wireless base station, but that multiple devices are grouped in a certain area and the application of the D2D communication to communication within the device group is also possible.
On the other hand, according to the D2D communication, it is possible to perform not only direct communication between the wireless terminals that use a radio resource which is managed or controlled by the wireless base station, but also the direction communication between the wireless terminals that does not use the radio resource which is managed or controlled by the wireless base station. Furthermore, many radio resources are relatively desired in order to use a modulation coding scheme (MCS) that is more resistant to an error in a case where the wireless terminal is positioned at the boundary of a cell, but a case where this problem is alleviated by applying the inter-terminal communication is also assumed. Because of this, the D2D communication also receives a lot of attention from the perspective of efficient usage of the radio resource, suppression of a processing load on the wireless base station, or the like.
The discussion on the D2D communication has just started in the 3GPP, and feasibility of the D2D communication, technologies that are desired to realize the D2D communication, performance and the like that are expected have been discussed so far. Furthermore, proximity services (ProSe) have been discussed that are broad concepts for the D2D communication or a service or application that is involved in the D2D communication. Because it is thought that the D2D communication is a technology that has applications in many fields, the D2D communication will expectedly continue to be actively discussed as a promising technology in the future in the 3GPP.